Quick 7 Day Method:
This quick, 7 day stratification technique is a good option if you are getting a start on stratification later in the season, but germination rates can be a bit lower than other stratification methods.
1) Ensure your seed requires cold and moist stratification. Some natives do not, so make sure to read your germination instructions carefully.
2) Grab a reusable container, and label the name of the plant, the date you started stratification and then I add in 4 check boxes under the word 'fridge' and another three check boxes under the word 'freezer'. Alternatively, you can use a plastic bag and permanent marker.
3) Combine your seed and a sterile medium (I like vermiculite and perlite) in your reusable container or bag and add enough water to wet the mixture, but not enough that there's water swishing around. You want the medium to be sterile, that is new or sterilized (by leaving it out in the sun for example) because you will be leaving the seed in a moist environment long enough for mold to form otherwise, which can kill your seed. I don't recommend using soil, sand or paper towel for this reason.
4) Ring out any excess water from your seed + sterile medium mix, either by squeezing the mix with your hands, or by squeezing the bag. Dump off any excess water.
5) Put your container or bag in the fridge for the first day.
6) On day two, put your container or bag in the freezer. I know I mention above not to put your seeds directly in the freezer, but the difference here is that you've already cooled them in the fridge, so in this case the additional cooling will be gradual and not damage the plant cells.
7) Alternate between fridge and freezer for 7 days, checking your seeds daily. Add additional water if required. If the seeds start to germinate, remove all of them from the fridge and plant.
6) Either at the end of your stratification period, or when your seeds begin to germinate (whichever comes first), plant your seeds, along with the vermiculite or perlite if you wish. No need to separate the seeds from the mixture.
Don't worry if some or none of the seeds germinate by the end of the stratification period, many species don't at all. Plant your seeds indoors under a grow light or in a full sun window, or in a prepared seedbed outdoors. In terms of when to plant in the spring, many wildflower seedlings are frost tolerant, but it's overall best to wait until the risk of frost has passed since this will ensure the healthiest plants.
7) Care for your seeds as prescribed on your seed packs and enjoy watching them grow.
Here's a simplified version for quick reference:
Regular Fridge Method:
This method is typically best started about 8 weeks before your last frost, or 8 weeks before you wish to start your seeds indoors. For the least amount of steps and fuss, plan to direct sow your seeds outside after the stratification process is complete, which means wait to start the fridge stratification 8 weeks before your last frost date.
Note that some species require longer cold periods, these are just general guidelines. Always refer to the cold stratification period noted on the back of our seed packets, or research online to determine if a longer cold period is necessary.
1) Ensure your seed requires cold and moist stratification. Some natives do not, so make sure to read your germination instructions carefully.
2) Grab a reusable container and label with the name of the plant, the date you started stratification and the approximate date you are to remove the seeds for planting. To figure this out, check the back of your seed packet to see how long stratification is required, for most species 6-8 weeks is enough. Alternatively, you can use a plastic bag and permanent marker.
3) Combine your seed and a sterile medium (I like vermiculite and perlite) in your reusable container or bag. Add enough water to wet the mixture, but not enough that there's water swishing around. You want the medium to be sterile, that is new or sterilized (by leaving it out in the sun for example) because you will be leaving the seed in a moist environment long enough for mold to form otherwise, which can kill your seed. I don't recommend using soil, sand or paper towel for this reason.
4) Ring out any excess water from your seed + sterile medium mix, either by squeezing the mix with your hands, or by squeezing the bag. Dump off any excess water.
5) Put your container or bag in the fridge sealed fir the specified time (usually about 8 weeks). Check on your seeds regularly for signs of germination and to add water if necessary.
6) Either at the end of your stratification period, or when your seeds begin to germinate (whichever comes first), plant your seeds, along with the vermiculite or perlite if you wish. No need to separate the seeds from the mixture.
Don't worry if some or none of the seeds germinate by the end of the stratification period, many species don't at all. Plant your seeds indoors under a grow light or in a full sun window, or in a prepared seedbed outdoors. In terms of when to plant in the spring, many wildflower seedlings are frost tolerant, but it's overall best to wait until the risk of frost has passed since this will ensure the healthiest plants.
7) Care for your seeds as prescribed on your seed packs and enjoy watching them grow.
For more methods of stratifying seeds, visit this page.
To learn why we recommend vermiculite as the ideal medium for this, check out this blog post.
